Data storage device and a method of generating a motor control signal therefor

ABSTRACT

The invention relates to a data storage device ( 101 ) which comprises a data interface ( 103 ) for reading data from a spinning data storage disc ( 105 ). The data storage device ( 101 ) comprises a motor (111) for spinning the data storage disc ( 105 ) at a desired speed. The data storage device ( 101 ) further comprises a speed change processor ( 115 ) for determining a preferred motor speed change time; and a motor controller ( 113 ) for controlling the motor ( 111 ) to perform the speed change in response to the preferred motor speed change time. Specifically, the preferred motor speed change time resulting in the lowest energy consumption for disc spin-up and jump operations are determined, and the motor ( 111 ) is controlled to change the speed substantially within the preferred motor speed change time. The invention is particularly suitable for Small Form Factor Optical (SFFO) disc systems and allows for reduced energy consumption and thus increased battery life.

The invention relates to a data storage device and a method ofgenerating a motor control signal therefore and in particular for a datastorage device for a spinning data storage disc.

In recent years, there has been a general trend towards reduced size andincreased mobility for much consumer equipment. For example, the use ofportable phones, computers, personal music systems and personal digitalAssistants (PDAs) have become increasingly widespread.

Typically, these small portable devices comprise significant amount ofcomputational resources and are capable of processing large amounts ofdata. Furthermore, most devices comprise means for reading data from orwriting data to external removable data media.

An example of a very high-density removable data storage medium is anoptical disc, and it is therefore desirable in many small devices toinclude a data storage device for reading or writing optical discs.

As many small portable devices are limited by the available energysupply, which is typically only available from rechargeable batterieshaving a limited capacity, one of the most important parameters forportable devices is their power consumption. In order to achieve a longbattery life and a small physical size of the batteries, it is essentialto reduce the energy consumption of the components as much as possible.

However, motors typically have relatively high power consumption. A datastorage device accessing a removable storage medium, such as an opticaldisc, inherently requires a motor to spin the optical disc during thereading or writing operations. However, this tends to result in arelatively high power consumption, and in particular the energyconsumption associated with spin-up of the disc and jumps betweendifferent reading or writing positions is significant.

Accordingly, a data storage device having increased motor control and/ora reduced power/energy consumption is advantageous. In particular, adata storage device having means for operating a motor of the datastorage device with lower energy consumption would be advantageous.

Accordingly, the invention seeks to provide an improved data storagedevice and method of generating a motor control signal system for motorcontrol, and preferably seeks to mitigate, alleviate or eliminate one ormore of the above-mentioned disadvantages singly or in any combination.

According to a first aspect of the invention, there is provided a datastorage device comprising:

-   -   a data interface for transferring data from or to a spinning        data storage disc at a first data rate;    -   a motor for spinning the disc;    -   means for determining a preferred motor speed change time; and    -   motor control means for controlling the motor to perform the        speed change in response to the preferred motor speed change        time.

The inventors of the current invention have realized that a number ofparameters may depend on the motor speed change time, and that animproved performance can be achieved by controlling the motor to changespeed in response to a preferred motor speed change time. The inventionenables an improved control of motor associated parameters for a datastorage device thereby allowing for improved performance of the datastorage device. The motor speed may specifically be a rotationalfrequency associated with a reading or writing position of the datastorage disc. The data storage device may specifically be a data readingdevice for reading data from the disc, a data writing device for writingdata unto the disc or a combined reading and writing device capable ofboth reading and writing data from and to the disc.

According to a feature of the invention, the means for determining isoperable to determine the preferred motor speed change time in responseto at least one energy consumption associated with the preferred motorspeed change time.

Preferably, the preferred motor speed change time is determined suchthat energy consumption is reduced or minimized. The preferred motorspeed change time may specifically be determined by determining theenergy consumption of all or parts of the data storage device as afunction of the preferred motor speed change time and selecting thepreferred motor speed change time as that resulting in the lowest energyconsumption. Hence battery life and/or size of the data storage devicemay be improved.

According to another feature of the invention, the at least one energyconsumption comprises an energy consumption of the motor.

The inventors have realized that for very slow speed changes of a motor,a high energy consumption results due to the long time it takes for themotor to reach the desired speed. Typically, data cannot be read from orwritten to the disc during the speed change interval, while at leastpart of the system does consume energy. Furthermore, the inventors haverealized that for very fast motor speed changes, energy consumptionincreases due to increased losses of the motor. The invention allows fora preferred motor speed change time to be determined in response tothese parameters whereby a reduction or optimization of powerconsumption of the motor can be achieved. As the energy consumption of amotor typically is one of the most significant energy consumptions of adata storage device, a significant reduction of the energy consumptionof the entire data device is achieved thereby enabling extended batterylife and/or reduced size of the data storage device.

According to another feature of the invention, the data storage devicefurther comprises an output buffer coupled to the data interface andoperable to receive data from the data interface at the first data ratein a first time interval and to output data at a lower data rate for alonger time interval.

Data may typically be read from a data storage disc at much higher datarates than required from the data storage device, and an output bufferallows for rate adjustment between these. Specifically, the outputbuffer may allow that the motor is only active during the first timeinterval thereby allowing for a significant power reduction. This willhowever result in an uneven non-continuous operation of the motor andthereby in many motor speed changes. Therefore, controlling the motor inresponse to a preferred motor speed change time will in this case be ofparticular importance.

According to another feature of the invention, the at least one energyconsumption comprises a first energy consumption associated with thefirst time interval and a second energy consumption associated with thesecond time interval.

This allows for the preferred motor speed change time to be optimizedwhile allowing a trade off between the lengths of the individualintervals and thus allows for an improved energy consumption reduction.The at least one energy consumption may be the energy consumption of thewhole interval but is preferably the energy consumption of asub-interval. This sub-interval may be of a constant size such that theenergy consumption corresponds to a power consumption or may be theenergy consumption of a time interval which is either part of the firstor second time interval depending on the value of the preferred motorspeed change time.

According to another feature of the invention, the data storage devicefurther comprises means for reducing the energy consumption of the motoroutside the first interval and the second energy consumption is anenergy consumption of the data storage device when the energyconsumption of the motor is reduced. Preferably, the first energyconsumption may comprise an energy consumption of the data storagedevice excluding an energy consumption of the motor. The first energyconsumption may specifically comprise a first component corresponding tothe energy consumption of the data storage device excluding an energyconsumption of the motor and a second component corresponding to theenergy consumption of the motor.

Preferably, the preferred motor speed change time is determined inresponse to the energy consumption in time intervals when the motor isactive and intervals when the motor is not active. The power consumptionin each time interval is typically significantly different and bycontrolling the motor speed change time in response to the preferredmotor speed change time, when taking into account the different energyconsumptions in the different time intervals, provides increasedpossibility of optimizing the control of the motor and thus theperformance of the data storage device.

According to another feature of the invention, the data storage devicefurther comprises means for measuring at least one energy consumptionparameter of an element of the data storage device and the at least oneenergy consumption comprises the at least one energy consumptionparameter.

Preferably, the at least one energy consumption parameter may bemeasured real time or sufficiently frequently for the measured value tobe a reasonable representation of the current conditions of the elementof the data storage device. The energy consumption of the element ispreferably determined from the measured parameter. The energyconsumption parameter may for example be a current drawn by the motor indifferent operating conditions. The energy consumption parameter mayalso be an indirect parameter, such as an operating temperature,wherefrom an energy consumption can be calculated or estimated.

This allows for a highly efficient operation of the motor which may bedynamically adapted to the currently prevailing conditions.Significantly reduced power consumption may be achieved.

According to another feature of the invention, the preferred motor speedchange time is a disc spin up time. The spin up of a disc is aparticularly frequent and energy consuming operation and therefore aparticular advantageous energy consumption reduction may be achieved bydetermining a preferred motor speed change time for this operation.

According to another feature of the invention, the motor speed isdependent on the disc access position and the preferred motor speedchange time is associated with a step change in the disc access positionbetween a first disc access position and a second disc access position.The disc access positions may specifically be disc reading positions ordisc writing positions.

In this case the preferred motor speed change time may be considered ajump time for the data storage device jumping from one access positionto another. The jump time is a particularly frequent and energyconsuming operation and therefore a particular advantageous energyconsumption reduction may be achieved by determining a preferred motorspeed change time for this operation.

According to another feature of the invention, the means for determiningis operable to determine the preferred motor speed change time inresponse to a rotational frequency difference between a first rotationalfrequency of the disc associated with the first disc access position anda second rotational frequency of the disc associated with the secondaccess position.

Motor parameters, such as the energy consumption of the motor, maytypically be particularly sensitive and dependent on the amount of thechange between different operating conditions. Determining the preferredmotor speed change time in response to a step in rotational frequencyallows for the optimal value of the preferred motor speed change time tobe determined for the specific jump size (e.g. the size of the stepchange in rotational frequency). The first rotational frequency mayspecifically be a rotational frequency when the motor is not active andmay specifically be substantially zero.

According to another feature of the invention, the data storage devicefurther comprises a data storage comprising associations between thepreferred motor speed change time and the rotational frequencydifference and the means for determining is operable to determine thepreferred motor speed change time by accessing the data storage.

This provides for a low complexity implementation of means fordetermining the preferred motor speed change time. It furthermore allowsfor the relationship between the preferred motor speed change time andthe rotational frequency difference to be stored in the data storagedevice during manufacture.

According to another feature of the invention, the data storage devicefurther comprises:

-   -   means for outputting information related to the preferred motor        speed change time;    -   input means for receiving motor control information; and    -   the motor control means is operable to control the motor in        response to the motor control information.

This allows for external means to control or assist in the control ofthe motor. For example, this may allow an application to select a tradeoff between energy consumption and other parameters to suit the specificapplication. It may for example allow for the preferred motor speedchange time to be dependent on the remaining battery life for a devicecomprising the data storage device. Hence, improved performance of anapplication or device comprising the data storage device may beachieved.

According to another feature of the invention, the motor control meansis further operable to control the motor in response to the data readfrom the data storage disc.

This allows, for example, for a motor operation dependent on which discis being read or allows for an application to control or assist in thecontrol of the motor. Thus, specifically, an application utilizing thedata from the data storage disc may implement all or part of the controlmeans.

According to another feature of the invention, the data storage deviceis an optical data storage device and the data storage disc is anoptical storage disc.

This allows for a highly efficient optical disc storage device havinglow energy consumption. The data storage device may specifically be aSmall Form Factor Optical (SFFO) disc reader.

According to a second aspect of the invention, there is provided amethod of generating a motor control signal for a data storage devicehaving a motor for spinning a data storage disc; the method comprisingthe steps of: transferring data to or from the data storage disc at afirst data rate; determining a preferred motor speed change time; andgenerating a motor control signal operable to control the motor toperform the speed change in response to the preferred motor speed changetime.

These and other aspects, features and advantages of the invention willbe apparent from and elucidated with reference to the embodiment(s)described hereinafter.

An embodiment of the invention will be described, by way of exampleonly, with reference to the drawings, in which:

FIG. 1 illustrates a block schematic of a data storage device inaccordance with an embodiment of the invention;

FIG. 2 illustrates an operational cycle for a data storage device inaccordance with an embodiment of the invention;

FIG. 3 illustrates an example of power consumption during differentphases of a data storage device in accordance with an embodiment of theinvention;

FIG. 4 illustrates an example of an energy consumption as a function ofa preferred motor speed change time for a disc jump in a data storagedevice in accordance with an embodiment of the invention; and

FIG. 5 illustrates an example of an energy consumption as a function ofa preferred motor speed change time for a disc spin up in a data storagedevice in accordance with an embodiment of the invention.

The following description focuses on an embodiment of the inventionapplicable to a data storage device for an optical storage disc, such asa CD, DVD or in particular a Small Form Factor Optical (SFFO) disc.However, it will be appreciated that the invention is not limited tothis application and may be used in association with many other datastorage devices including for example data storage devices for magneticstorage discs or magneto-optical storage discs.

The following description will focus on an embodiment applicable to adata reading device wherein data is transferred from the storage discbut it will be apparent that the invention is equally applicable to forexample a data-writing device wherein data is transferred to the storagedisc.

FIG. 1 illustrates a block schematic of a data storage device 101 inaccordance with a preferred embodiment of the invention.

In accordance with the preferred embodiment of the invention, the datastorage device 101 comprises a data interface 103 which is operable toread data from a spinning data storage disc, which in the preferredembodiment is an optical disc 105. In the preferred embodiment, the datastorage device 101 is a Small Form Factor Optical (SFFO) data storagedevice and the optical disc 105 is an SFFO disc.

It will be apparent, that the data storage device 101 comprises thenecessary mechanical arrangement for loading, securing and unloading theoptical disc during operation. Any suitable mechanical arrangement maybe used, and the person skilled in the art may apply any suitableapproach or design criteria suitable for the specific application.Various mechanical arrangements for implementation of data storagedevices for spinning storage discs are well known in the art and willfor the sake of clarity and brevity not be described further here.

The data interface 103 comprises means for reading data from a spinningoptical disc 105 by reading the stored optical information using alaser. The optical data is converted into an electrical data signal. Thedata interface 103 may further comprise error correcting functionalityas is well known in the art. In the preferred embodiment, the datainterface 103 is coupled to an output buffer 107.

The data read from the optical disc is typically a discontinuous datastream, wherein intervals of outputting data are separated by intervalswherein no data is output from the data interface 103. These non-activeintervals may for example correspond to intervals required for changingthe reading position on the disc, for spinning up the disc etc.Specifically, the data rate at which data is read from the disc may besignificantly higher than the output rate required from the data storagedevice, and therefore data may be read from the disc in short burstsinterspersed by non-active power down intervals. The output bufferprovides for a continuous data output and allows for the rate adaptationbetween the maximum data rate of the data interface 103 and the averagedata rate of the buffer output.

In other embodiments, the data storage device 101 does not comprise anoutput buffer and instead a discontinuous data stream may be output fromthe data interface.

The output buffer 107 further comprises an interface suitable foroutputting the data stream to an external source, such as for example acomputer, a PDA, a personal music system or a mobile phone.

The data storage device 101 also comprises a motor 111 for spinning theoptical disc 105. Any suitable arrangement may be used for enabling themotor to spin the disc, but in the preferred embodiment, the axis of themotor is rotationally and mechanically coupled to a spindle to which theoptical disc 105 is secured. In the preferred embodiment, there is adirect correspondence between the speed or rotational frequency of theoptical disc 105 and the speed or rotational frequency of the motor 111.

In the preferred embodiment, the motor is connected to a motorcontroller 113 which is operable to control the motor and specificallythe speed (or rotational frequency) of the motor and thereby the speed(or rotational frequency) of the spinning disc. Specifically, the motorcontroller 113 is operable to generate an electrical voltage and/orcurrent which when applied to the motor 111 will cause the motor 111 tohave the desired speed. The motor speed may thus be dynamicallycontrolled by the motor controller 113 dynamically varying the value ofthe electrical control signal.

In the preferred embodiment, the motor controller 113 comprisesmeasurement means, control loop feed back means etc for ensuring asuitable motor speed during data reading operations as is well known inthe art. Specifically during a data reading operation, the motorcontroller 113 may receive control feed back from the data storagedevice. The feedback may be used to control the motor speed such thatthe rotational frequency of the spinning disc is suitable for thecurrent data reading position.

The motor controller 113 is in the preferred embodiment coupled to aspeed change processor 115 operable to determine a preferred motor speedchange time. Thus in the preferred embodiment, when a speed change ofthe motor is required by the data storage device 101, for example whenthe motor is restarted following an inactive interval, the speed changeprocessor 115 is activated. It then proceeds to determine the preferredduration for the motor to change the speed from the current speed to thedesired speed. This preferred motor speed change time is then fed to themotor controller 113 which is operable to control the motor 111 toachieve the motor speed change in substantially the preferred motorspeed change time.

The inventors have realized that many parameters associated with achange in the speed of a motor depend on the duration of the speedchange, and that advantageous performance can be achieved by controllingthe motor of a data storage device in response to the preferred motorspeed change time. For example, the value of a specifically criticalparameter may be determined as a function of the motor speed changetime, and a preferred time for the motor speed change may be determinedas that resulting in the optimal value of the critical parameter. Themotor may subsequently be controlled to achieve the motor speed changein substantially that time, thereby resulting in the optimal effect onthe critical parameter.

It will be appreciated that any suitable parameter, criteria oralgorithm may be used for determining the preferred motor speed changetime. However, in the preferred embodiment, the preferred motor speedchange time is determined in response to one or more energy consumptionsassociated with the preferred motor speed change time.

For example, an energy consumption of the motor may be determined inresponse the preferred motor speed change time. An extremely short motorspeed change time requires that high voltages and/or currents be fed tothe motor thereby resulting in increased losses and thus a relativelyhigh-energy consumption. However, for long motor speed change times, themotor is operational for a long time (during which data are not readfrom the disc) and accordingly the energy consumption of this intervalwill become high.

Therefore, an optimal motor speed change time exists at which the energyconsumption is minimum.

In one embodiment, the motor may be pre-characterized such that the lossmay be predetermined for different motor speed change times. In thiscase, the speed change processor 1 15 may simple determine the preferredmotor speed change time in response to a table look up. In otherembodiments, parameters and characteristics of the motor may be storedand used by the speed change processor 1 15 to calculate the preferredmotor speed change time.

In the preferred embodiment, the output buffer allows for the data fromthe data interface to be received at a first data rate in a first timeinterval. The data may be outputted at a lower data rate for a longertime interval. For example, the data rate from the data interface 103may be ten times higher than the output data rate of the output buffer107. In this example, data may only be read for approximately 10% of thetime and the motor may be shut down for the remaining time. Thepreferred motor speed change time may in this case be determined bytaking into account the different power or energy consumption in thedifferent time intervals. Thus, the preferred motor speed change timemay for example be determined in response to the relative energyconsumption in different intervals corresponding to different operatingconditions of the data storage device.

Specifically, the preferred motor speed change time may be determined inresponse to energy consumption in an interval wherein the motor isactive compared to a time intervals wherein the motor is operating at areduced power or specifically when the motor is shut down.

In the preferred embodiment, the preferred motor speed change time isdetermined for a disc spin up time. For a data storage device with anoutput buffer operating in a discontinuous mode as described, the motoris shut down in every cycle, and thus whenever a new reading operationis initiated, the disc must initially be spun up to the desiredrotational frequency. The energy consumption of this spin up will dependon the preferred motor speed change time, and therefore the energyconsumption of this interval may be minimized by determining thepreferred motor speed change time.

In the preferred embodiment, a preferred motor speed change time isadditionally determined for jump times associated with the data readingoperation. In many optical disc reading systems, the disc reading datarate is constant. As the radius of the disc reading position varies,this results in the rotational frequency of the disc being dependent onthe reading position. Thus, typically, the motor speed is dependent onthe disc reading position and step changes in the disc reading positionbetween a first disc reading position and a second disc reading positionmay occur. When such a jump occurs in the reading position, a speedchange of the motor is required. Such jumps may occur many times duringa single disc reading interval. In accordance with the preferredembodiment of the invention, the preferred motor speed change time forsome or all of these jumps are determined and the motor is controlledaccordingly.

Specifically, the preferred motor speed change time is preferablydetermined at least in response to characteristics of the motor and therotational frequency difference between a first rotational frequency ofthe disc associated with the first disc reading position and a secondrotational frequency of the disc associated with the second readingposition. Thus, when a jump in reading position is required, theinformation is passed to the speed change processor 115 which determinesthe preferred motor speed change time as that which results in thelowest energy consumption of the jump taking into account the motorcharacteristics and the difference in rotational frequency required fora jump from the first reading position to the second reading position(as well as e.g. the energy consumption of other parts of the datastorage device). For example, if the difference in rotational frequencyis low, a short preferred motor speed change time may be determined andif the change in rotational frequency is high, a longer preferred motorspeed change time may be determined.

In one embodiment, the speed change processor 115 may comprise a look uptable comprising associations between the preferred motor speed changetime and the rotational frequency difference. In this embodiment, thespeed change processor 115 is operable to determine the preferred motorspeed change time by accessing the data storage.

Specifically, the look up table may comprise different jump distancesassociated with the most energy efficient jump times. Entries to thistable can be calculated from a motor power curve and the power valuesfrom other parts of the system. The values may be calculated real timebut are preferably precalculated and stored in the table duringmanufacture. When a jump is required, the most power efficient jump timeis fetched from this table by the speed change processor 115 and used asthe preferred motor speed change time.

In some embodiments, the data storage device further comprises means formeasuring at least one energy consumption parameter of an element of thedata storage device. For example parameters associated with the power orenergy consumption of the motor and/or other parts of the data storagedevice may be measured real time and used to calculate the preferredmotor speed change time. This will allow for the preferred motor speedchange time to be calculated while taking into account the actual ratherthan predicted values of various energy consumption parameters.

The measurement is preferably a direct measurement of power or energyconsumption, such as for example a measurement of the current drain ofthe motor for different motor speed change times. Thus, whenever a motorspeed change occurs, the energy consumption of the motor may be measuredand used to continuously update data associating motor energyconsumption and motor speed change times. In other embodiments, anindirect measure may be performed. For example, different power curvesmay exist for a motor dependent on the temperature of the motor.Accordingly, the temperature of the motor may be measured and used toderive a motor energy consumption.

A specific example of an embodiment directed to a small form factoroptical (SFFO) disc system for portable applications is described inmore detail in the following. For such an application it is importantthat the data storage device has very small dimensions (e.g. 36.4×42.8×5mm). Furthermore, the storage capacity of the discs should be high (1 GBor higher), and the power dissipation of the data storage device shouldbe low. To keep the dissipation as low as possible, it is advantageousto use knowledge of the power dissipation of different parts of the datastorage device at certain times. The specific embodiment is directed toa reduction of power during jumps to different locations on the discwhen reading or writing a file and during spin-up of the disc justbefore reading or writing.

For SFFO streaming applications, the bit rates are typically in theorder of 0.5 to 1 Mbps, while the data storage device is typicallycapable of handling data rates up to 36 Mbps. To save power it istherefore advantageous to use an output buffer. Once in a while, thebuffer is filled at a data rate of 36 Mbps, after which the data storagedevice is stopped almost completely to allow the buffer to be read outat a rate of e.g. 1 Mbps (the application data rate). This way the datastorage device is only active during part of the time, which results ina significant power reduction. This approach leads to a data storagedevice that has an operational cycle containing a certain number ofphases. For instance, the cycle may comprise a spin up phase in whichthe spindle motor accelerates the disc to the desired rotationalfrequency, an initializing optics phase in which the optics areinitialized before read/write, a (number of) search phase(s) in whichthe correct physical address on the disc is searched, a (number of)read/write phase(s), a (number of) jump phase(s) in which a jump is madeto a different location on the disc and finally a buffer phase in whichthe data storage device is largely inactive while the buffer is readout.

FIG. 2 illustrates an operational cycle for a data storage device inaccordance with this approach. FIG. 2 illustrates one cycle, which isdivided in the different phases. FIG. 2 thus illustrates an example of acycle comprising a spin up phase 201, an initializing optics phase 203,a (number of) search phase(s) 205, a (number of) read/write phase(s)207, a (number of) jump phase(s) 209 and a buffer phase 211 (FIG. 2illustrates the different jump/search/read/write phases groupedtogether. For example, if a plurality of jumps occurs these are allgrouped together in phase 209 and thus the total duration of phase 209is the total jump time per cycle (i.e. the sum total of the individualjump times of all jumps in the cycle)).

FIG. 3 illustrates an example of the power consumption during thedifferent phases illustrated in FIG. 2 (and arranged in the same orderas in FIG. 2). As can be seen, the power consumption during the bufferinterval 201 is significantly lower than the power consumption duringthe phases in which the motor is active. The energy consumption of eachinterval or phase may be determined by multiplying the power consumptionillustrated in FIG. 3 by the duration of the phase as illustrated inFIG. 2.

In the following, a specific example of how the preferred motor speedchange time may determined for the specific embodiment is given.Specifically, a preferred motor speed change time for a jump timeassociated with a step change in the reading position between a firstreading position and a second reading position is given.

The preferred jump time depends on the desired rotational frequency, theacceleration of the spindle motor and the number of jumps to be takenper cycle. For a given cycle time (given by the user data rate and thebuffer size), an increment of the jump time means a reduction of thebuffer time (i.e. it is assumed that the other times are substantiallyfixed). Since the jump power is much higher than the buffer power, it ispreferable to make the jump time as short as possible. However, forconstant linear velocity (CLV) systems (i.e. systems in which datapasses the laser spot with the same velocity regardless of the readingposition), a small jump time means that the acceleration/deceleration ofthe spindle motor needs to be performed very fast thereby increasing theenergy dissipation in the motor and motor driver during the jump. Tofind the lowest energy consumption, the following equation needs to besolved:E _(jump,CLV)=min((P _(system,jump) −P _(system,buffer) +P _(motor,spin)_(—) _(up/down)(t))t _(jump))wherein:

-   -   t_(jump) is the preferred duration of the jump phase;    -   P_(system,jump) is the power consumption of all parts of the        data storage device, except the motor, that are active during a        jump;    -   P_(system,jump) is the power consumption of all the parts of the        data storage device that are active during the buffer phase; and    -   P_(motor,spin) _(—) _(up/down) is the power consumed in the        motor, given that the spin-up/down of the motor during a jump        has to be achieved in t_(jump). This is of course dependent on        the required change in motor frequency, and thus the jump        distance.

The preferred motor speed change time t_(jump) can be found as follows.

First the motor power is calculated as a function of time:$\begin{matrix}{{P_{mot}(t)} = {iu}} \\{= {i\left( {{iR}_{e} + V_{backEMF}} \right)}} \\{= {{i^{2}R_{e}} + {iV}_{backEMF}}} \\{= {{\left( \frac{T_{air} + T_{bearing} + T_{{spin} - {up}}}{K_{t}} \right)^{2}R_{e}} +}} \\{\frac{T_{air} + T_{bearing} + T_{{spin} - {up}}}{K_{t}}V_{backEMF}} \\{= {{\left( \frac{T_{air} + T_{bearing} + \frac{J_{tot}\varpi_{ttm}}{t}}{K_{t}} \right)^{2}R_{e}} +}} \\{\frac{T_{air} + T_{bearing} + \frac{J_{tot}\varpi_{ttm}}{t}}{K_{t}}V_{backEMF}} \\{= {{\left( {\frac{T_{air} + T_{bearing}}{K_{t}} + \frac{J_{tot}\varpi_{ttm}}{K_{t}t}} \right)^{2}R_{e}} +}} \\{\frac{\left( {T_{air} + T_{bearing}} \right)V_{backEMF}}{K_{t}} + {\frac{J_{tot}\varpi_{ttm}}{K_{t}t}V_{backEMF}}} \\{= {{\left( \frac{T_{air} + T_{bearing}}{K_{t}} \right)^{2}R_{e}} + \frac{\left( {T_{air} + T_{bearing}} \right)V_{backEMF}}{K_{t}} +}} \\{{\left( {{\frac{2\left( {T_{air} + T_{bearing}} \right)}{K_{t}^{2}}R_{e}} + \frac{V_{backEMF}}{K_{t}}} \right)J_{tot}{\varpi_{ttm} \cdot \frac{1}{t}}} +} \\{\left( \frac{J_{tot}\varpi_{ttm}}{K_{t}} \right)^{2}{R_{e} \cdot \frac{1}{t^{2}}}}\end{matrix}$wherein:

-   -   T_(air) is the air friction torque;    -   T_(bearing) is the bearing friction torque;    -   J_(tot) is the total inertia of disc, hub and motor;    -   ω_(ttm) is the total change in rotational frequency in a jump;    -   K_(t) is a motor constant;    -   Re is the electrical resistance of the motor, and    -   V_(backEMF)=K_(t) ^(≠ω) _(ttm).        Setting        $a = {{\left( \frac{T_{air} + T_{bearing}}{K_{t}} \right)^{2}R_{e}} + \frac{\left( {T_{air} + T_{bearing}} \right)V_{backEMF}}{K_{t}}}$        $b = {\left( {{\frac{2\left( {T_{air} + T_{bearing}} \right)}{K_{t}^{2}}R_{e}} + \frac{V_{backEMF}}{K_{t}}} \right)J_{tot}\varpi_{ttm}}$        $c = {\left( \frac{J_{tot}\varpi_{ttm}}{K_{t}} \right)^{2}R_{e}}$        yields ${P_{mot}(t)} = {a + \frac{b}{t} + \frac{c}{t^{2}}}$        The total (extra) energy used during a jump is given by,        $\begin{matrix}        {{E_{tot}(t)} = {{P_{mot}(t)}{t\left( {P_{{system},{jump}} - P_{{system},{buffer}}} \right)}t}} \\        {= {{\left( {a + P_{{system},{jump}} - P_{{system},{buffer}}} \right)t} + b + \frac{c}{t}}}        \end{matrix}$        To find the minimum the first derivative of the above equation        is determined:        $\frac{{dE}_{tot}(t)}{t} = {\left. 0\Leftrightarrow 0 \right. = {\left. {\left( {a + P_{{system},{jump}} - P_{{system},{buffer}}} \right) - \frac{c}{t^{2}}}\Leftrightarrow t \right. = \sqrt{\frac{c}{a + P_{{system},{jump}} - P_{{system},{buffer}}}}}}$

Hence, the preferred motor speed change time may be determined from thedescribed parameters and motor characteristics.

The calculation may be made more accurate by talking further parametersinto account. For example, in the described calculation, the motordriver power consumption is not taken into account In other embodiments,simpler calculations may be performed and fewer parameters taken intoaccount.

FIG. 4 illustrates an example of the energy consumption as a function ofa preferred motor speed change time for a data storage device inaccordance with an embodiment of the invention. In FIG. 4, curve 401illustrates the energy consumption of the motor as a function of thejump time. Curve 401 shows a decrease in energy usage when the availablejump time gets longer. Curve 403 illustrates the energy consumption ofthe system except the motor. The power difference between the jump- andbuffer-phase for the system except motor is constant, thereforeresulting in a linearly increasing curve for the extra energy usage as aresult of a jump for a given jump time. Curve 405 illustrates the totalenergy usage in the data storage device during a jump as a function ofthe jump time length. As can be seen, the energy consumption has a clearminimum corresponding to a certain jump time.

The most energy efficient spin-up time can be found in a similar way bydetermining the energy minimum and the corresponding preferred motorspeed change time t_(spin-up):E _(spin) _(—) _(up)=min((P _(system,spin-up) −P _(system,buffer) +P_(motor,spin) _(—) _(up/down)(t))t _(spin-up))

FIG. 5 illustrates an example of the energy consumption as a function ofa preferred motor speed change time for a disc spin up in a data storagedevice 101 in accordance with an embodiment of the invention. The totalenergy consumption is illustrated by curve 501 and clearly shows aminimum.

The most energy efficient spin-up time is generally larger than the mostenergy efficient jump time. The reason for this, is that during spin up,a smaller fraction of the total system needs to be active than during ajump, i.e. the difference in system power between buffer and spin-upphase is smaller than between buffer and jump phase, allowing the motorto take more time to perform the spin-up. In other words, for a spin up,the power dissipation of the motor plays a larger role in the totaldissipation than for a jump.

In some embodiments, the data storage device may further comprise acontrol output interface, for outputting information related to thepreferred motor speed change time, and a control input interface forreceiving motor control information. In these embodiments, the motorcontroller 113 is operable to further control the motor in response tothe motor control information received by the input means.

Specifically, various tables and characteristics used by the speedchange processor 115 in determining the preferred motor speed changetime may be made accessible to an application using the data storagedevice. This will allow the application to influence the behavior of thedata storage device. Hence, the application using the data storagedevice 101 may specifically perform the trade offs between differentparameters, such as for example between energy consumption and datarates.

In some embodiments, the motor control means is further operable tocontrol the motor in response to the data read from the optical disc.For example, an application may be retrieved from the optical disc andthis application may comprise all or part of the described functionalityof the motor controller 113 and the speed change processor 115. Thusspecifically, the application may operate the motor of the data storagedevice thereby allowing for increased flexibility.

The invention can be implemented in any suitable form includinghardware, software, firmware or any combination of these. However,preferably, the invention is at least partially implemented as computersoftware running on one or more data processors and/or digital signalprocessors. The elements and components of an embodiment of theinvention may be physically, functionally and logically implemented inany suitable way. Indeed the functionality may be implemented in asingle unit, in a plurality of units or as part of other functionalunits. As such, the invention may be implemented in a single unit or maybe physically and functionally distributed between different units andprocessors.

Although the present invention has been described in connection with thepreferred embodiment, it is not intended to be limited to the specificform set forth herein. Rather, the scope of the present invention islimited only by the accompanying claims. In the claims, the termcomprising does not exclude the presence of other elements or steps.Furthermore, although individually listed, a plurality of means,elements or method steps may be implemented by e.g. a single unit orprocessor. Additionally, although individual features may be included indifferent claims, these may possibly be advantageously combined, and theinclusion in different claims does not imply that a combination offeatures is no feasible and/or advantageous. In addition, singularreferences do not exclude a plurality. Thus references to “a”, “an”,“first”, “second” etc do not preclude a plurality.

1. A data storage device (101) comprising: a data interface (103) fortransferring data from or to a spinning data storage disc (105) at afirst data rate; a motor (111) for spinning the data storage disc (105);means (115) for determining a preferred motor speed change time; andmotor control means (113) for controlling the motor (111) to perform aspeed change in response to the preferred motor speed change time.
 2. Adata storage device (101) as claimed in claim 1 wherein the means (115)for determining is operable to determine the preferred motor speedchange time in response to at least one energy consumption associatedwith the preferred motor speed change time.
 3. A data storage device(101) as claimed in claim 2 wherein the at least one energy consumptioncomprises an energy consumption of the motor (111).
 4. A data storagedevice (101) as claimed in claim 2 further comprising an output buffer(107) coupled to the data interface (103) and operable to receive datafrom the data interface (103) at the first data rate in a first timeinterval and to output data at a lower data rate for a longer timeinterval.
 5. A data storage device (101) as claimed in claim 4 whereinthe at least one energy consumption comprises a first energy consumptionassociated with the first time interval and a second energy consumptionassociated with the second time interval.
 6. A data storage device (101)as claimed in claim 5 further comprising means for reducing the energyconsumption of the motor (111) outside the first interval and the secondenergy consumption is an energy consumption of the data storage device(101) when the energy consumption of the motor (111) is reduced.
 7. Adata storage device (101) as claimed in claim 5 wherein the first energyconsumption is an energy consumption of the data storage device (101)excluding an energy consumption of the motor (111).
 8. A data storagedevice (101) as claimed in claim 2 further comprising means formeasuring at least one energy consumption parameter of an element of thedata storage device (101) and the at least one energy consumptioncomprises the at least one energy consumption parameter.
 9. A datastorage device (101) as claimed in claim 1 wherein the preferred motorspeed change time is a disc spin up time.
 10. A data storage device(101) as claimed in claim 1 wherein a motor speed is dependent on a discaccess position and the preferred motor speed change time is associatedwith a step change in the disc access position between a first discaccess position and a second disc reading position.
 11. A data storagedevice (101) as claimed in claim 1 wherein the means for determining (15) is operable to determine the preferred motor speed change time inresponse to a rotational frequency difference between a first rotationalfrequency of the data storage disc (105) associated with the first discaccess position and a second rotational frequency of the data storagedisc (105) associated with the second access position.
 12. A datastorage device (101) as claimed in claim 11 further comprising a datastorage comprising associations between the preferred motor speed changetime and the rotational frequency difference and the means fordetermining (1 15) is operable to determine the preferred motor speedchange time by accessing the data storage.
 13. A data storage device(101) as claimed in claim 1 further comprising means for outputtinginformation related to the preferred motor speed change time; inputmeans for receiving motor control information; and wherein the motorcontrol means (113) is operable to control the motor in response to themotor control information.
 14. A data storage device (101) as claimed inclaim 1 wherein the motor control means (113) is further operable tocontrol the motor in response to data read from the data storage disc(105).
 15. A data storage device (101) as claimed in claim 1 wherein thedata storage device (101) is an optical data storage device and the datastorage disc (105) is an optical storage disc.
 16. A method ofgenerating a motor control signal for a data storage device (101) havinga motor (111) for spinning a data storage disc (105), the methodcomprising the steps of: transferring data to or from the data storagedisc (105) at a first data rate; determining a preferred motor speedchange time; and generating a motor control signal operable to controlthe motor (111) to perform a speed change in response to the preferredmotor speed change time.
 17. A computer program enabling the carryingout of a method according to claim
 16. 18. A record carrier comprising acomputer program as claimed in claim 17.